This invention pertains to a method of polishing a substrate comprising a noble metal.
Compositions and methods for planarizing or polishing the surface of a substrate are well known in the art. Polishing compositions (also known as polishing slurries) typically contain an abrasive material in an aqueous solution and are applied to a surface by contacting the surface with a polishing pad saturated with the slurry composition. Typical abrasive materials include silicon dioxide, cerium oxide, aluminum oxide, zirconium oxide, and tin oxide. U.S. Pat. No. 5,527,423, for example, describes a method for chemically-mechanically polishing a metal layer by contacting the surface with a polishing slurry comprising high purity fine metal oxide particles in an aqueous medium. Alternatively, the abrasive material may be incorporated into the polishing pad. U.S. Pat. No. 5,489,233 discloses the use of polishing pads having a surface texture or pattern, and U.S. Pat. No. 5,958,794 discloses a fixed abrasive polishing pad.
Conventional polishing systems and polishing methods typically are not entirely satisfactory at planarizing semiconductor wafers. In particular, polishing compositions and polishing pads can have less than desirable polishing rates, and their use in the chemical-mechanical polishing of semiconductor surfaces can result in poor surface quality. Because the performance of a semiconductor wafer is directly associated with the planarity of its surface, it is crucial to use a polishing composition and method that results in a high polishing efficiency, uniformity, and removal rate and leaves a high quality polish with minimal surface defects.
The difficulty in creating an effective polishing system for semiconductor wafers stems from the complexity of the semiconductor wafer. Semiconductor wafers are typically composed of a substrate, on which a plurality of transistors has been formed. Integrated circuits are chemically and physically connected into a substrate by patterning regions in the substrate and layers on the substrate. To produce an operable semiconductor wafer and to maximize the yield, performance, and reliability of the wafer, it is desirable to polish select surfaces of the wafer without adversely affecting underlying structures or topography. In fact, various problems in semiconductor fabrication can occur if the process steps are not performed on wafer surfaces that are adequately planarized.
Various metals and metal alloys have been used to form electrical connections between interconnection levels and devices, including titanium, titanium nitride, aluminum-copper, aluminum-silicon copper, tungsten, platinum, platinum-tungsten, platinum-tin, ruthenium, and combinations thereof. Noble metals present a particular challenge in that they are mechanically hard and chemically resistant, making them difficult to remove efficiently through chemical-mechanical polishing.
The following patents disclose polishing compositions for noble metals. U.S. Pat. No. 5,691,219 discloses a semiconductor memory device comprising a noble metal conductive layer and a polishing composition comprising a halo-compound for polishing the noble metal. U.S. Pat. No. 6,274,063 discloses polishing compositions for nickel substrates comprising a chemical etchant (e.g., aluminum nitrate), abrasive particles, and an oxidizer. U.S. Pat. No. 6,290,736 discloses a chemically active polishing composition for noble metals comprising an abrasive and a halogen in basic aqueous solution. JP 63096599 A2 discloses a method of dissolving metallic ruthenium. JP 11121411 A2 discloses a polishing composition for platinum group metals (e.g., Ru, Pt) comprising fine particles of an oxide of the platinum group metal. JP 1270512 A2 discloses a dissolving solution for noble metals comprising hydrogen peroxide, alkali cyanide, and phosphate ion and/or borate ion. WO 00/77107 A1 discloses a polishing composition for noble metals (e.g., Ru, Rh, Pd, Os, Ir, Pt) comprising abrasive, a liquid carrier, an oxidizer, and a polishing additive including EDTA, nitrogen-containing macrocycles (e.g., tetraazacyclotetradecanes), crown ethers, halides, cyanides, citric acid, phosphines, and phosphonates. WO 01/44396 A1 discloses a polishing composition for noble metals comprising sulfur-containing compounds, abrasive particles, and water-soluble organic additives which purportedly improve the dispersion of the abrasive particles and enhance metal removal rates and selectivity.
A need remains, however, for polishing systems and polishing methods that will exhibit desirable planarization efficiency, uniformity, and removal rate during the polishing and planarization of substrates, while minimizing defectivity, such as surface imperfections and damage to underlying structures and topography during polishing and planarization. Improved polishing systems are particularly needed for the polishing of chemically stable and mechanically hard noble metal-containing substrates.
The present invention seeks to provide such a chemical-mechanical polishing system and method. These and other advantages of the invention will be apparent from the description of the invention provided herein.
The invention provides a method of polishing a substrate comprising (i) contacting a substrate comprising a noble metal with a chemical-mechanical polishing system comprising (a) an abrasive and/or polishing pad, (b) a liquid carrier, and (c) one or more polishing additives selected from the group consisting of diketones, diketonates, urea compounds, heterocyclic nitrogen-containing compounds, heteroclclic oxygen-containing compounds, heterocyclic phosphorus-containing compounds, nitrogen-containing compounds that can be zwitterionic compounds, salts thereof, and combinations thereof, wherein the chemical-mechanical polishing system has a pH of about 2 to about 12, and (ii) abrading at least a portion of the substrate to polish the substrate. The invention further provides a method of polishing a substrate comprising (i) contacting a substrate comprising a noble metal with a chemical-mechanical polishing system comprising (a) an abrasive and/or polishing pad, (b) a liquid carrier, (c) at least one polishing additive selected from metal compounds with two or more oxidation states, wherein the metal compound is soluble in the liquid carrier, and (d) a peroxy-type oxidizer, wherein the chemical-mechanical polishing system has a pH of about 2 to about 12, and (ii) abrading at least a portion of the substrate to polish the substrate. The invention additionally provides a method of polishing a substrate comprising (i) contacting a substrate comprising a noble metal with a chemical-mechanical polishing system comprising (a) xcex1-alumina and fumed alumina, (b) a polishing pad, and (c) a liquid carrier, wherein the weight ratio of xcex1-alumina to fumed alumina is about 0.6:1 to about 9:1.
The invention is directed to methods of polishing a substrate comprising a noble metal. The substrate is contacted with a chemical-mechanical polishing (xe2x80x9cCMPxe2x80x9d) system comprising (a) an abrasive and/or polishing pad, (b) a liquid carrier, and optionally (c) at least one polishing additive (i.e., one or more polishing additives). The polishing additive can be any suitable compound that desirably increases the rate at which the system polishes at least one noble metal layer of the substrate. At least a portion of the substrate is abraded so as to polish the surface of the substrate. The abrasive (when present and suspended in the liquid carrier), the liquid carrier, and optional polishing additive(s), as well as any other components suspended in the liquid carrier, form the polishing composition of the CMP system.
The CMP systems described herein comprise an abrasive, a polishing pad, or both. Preferably, the CMP systems comprise both an abrasive and a polishing pad. The abrasive can be fixed on the polishing pad and/or can be in particulate form and suspended in the liquid carrier. The polishing pad can be any suitable polishing pad.
The abrasive can be any suitable abrasive, many of which are known in the art. For example, the abrasive can be natural or synthetic and can comprise diamond (e.g., polycrystalline diamond), garnet, glass, carborundum, metal oxide, nitride, carbide, polymer, composite (e.g., polymer composite or polymer/metal oxide composite), and the like. The choice of abrasive can depend on the particular nature of the substrate being polished. The abrasive preferably comprises metal oxide, diamond, silicon carbide, silicon nitride, boron nitride, or combinations thereof. The metal oxide desirably is selected from the group consisting of alumina, silica, titania, ceria, zirconia, germania, magnesia, co-formed products thereof, and combinations thereof. More preferably, the abrasive comprises silica, alumina (e.g., xcex1-alumina, fumed alumina), silicon nitride, and/or silicon carbide.
When the abrasive is present in the CMP systems and is suspended in the liquid carrier (i.e., when the abrasive is a component of the polishing composition), any suitable amount of abrasive can be present in the polishing composition. Typically, about 0.01 wt. % or more (e.g., about 0.05 wt. % or more) abrasive will be present in the polishing composition. More typically, about 0.1 wt. % or more abrasive will be present in the polishing composition. The amount of abrasive in the polishing composition typically will not exceed about 50 wt. %, more typically will not exceed about 20 wt. %. Preferably, the amount of abrasive in the polishing composition is about 0.5 wt. % to about 10 wt. %.
A liquid carrier is used to facilitate the application of the abrasive (when present), one or more polishing additives, and any optional additives to the surface of a suitable substrate to be polished or planarized. The liquid carrier is typically an aqueous carrier and can be water alone, can comprise water and a suitable water-miscible solvent, or can be an emulsion. Suitable water-miscible solvents include alcohols such as methanol, ethanol, etc. Preferably, the aqueous carrier consists of water, more preferably deionized water.
In a first embodiment of the invention, a polishing additive is present in the chemical mechanical polishing system. The polishing additive interacts with the noble metal surface and promotes its dissolution during chemical-mechanical polishing. Suitable polishing additives include diketones, diketonates, urea compounds, heterocyclic nitrogen-containing compounds, heterocyclic oxygen-containing compounds, heterocyclic phosphorus-containing compounds, nitrogen-containing compounds that can be zwitterionic compounds, salts thereof, and combinations thereof.
Suitable diketones and diketonates include, for example, cyclopentanediones, cyclohexanediones, cyclobutanediones, cycloheptanediones, linear diketones, and alkylammonium-2,4-pentanedionate salts. Suitable heterocyclic nitrogen-containing compounds include, for example, pyridines, bipyridines, quinolines, phenanthrolines, pyrimidines, hydropyriridines, pyrazines, pyrazoles, imidazoles, imidazolines, imidazolidines, piperazines, triazines, purines, oxazoles, oxazines, pyrroles, pyrrolines, pyrrolidines, indoles, indolines, isoindoles, carbazoles, and combinations thereof. Suitable heterocyclic oxygen-containing compounds include, for example, dioxolanes, trioxolanes, furans, pyrones, morpholines, coumarins, benzopyrones, dioxanes, trioxanes, and ozonides. Suitable heterocyclic phosphorus-containing compounds include, for example, phospholes, phospholanes, phospholenes, and phospholidines. The heterocyclic nitrogen-, oxygen-, and phosphorus-containing compounds may further comprise one or more alcohol, amide, ketone, carboxylic acid, or sulfonic acid groups. For example, the heterocyclic nitrogen-containing polishing additives can be picolinic acid, 2-pyridinecarboxaldehyde, 3-pyridinecarboxaldehyde, 4-pyridinecarboxaldehyde, 2-pyridinemethanol, 2,3-pyridinedicarboxylic acid, 2,6-pyridinedicarboxylic acid, 2-pyridylacetic acid HCl, 3-pyridylacetic acid HCl, 2-pyridineethanesulfonic acid, 4-pyridineethanesulfonic acid, 1-(3-sulfopropyl)pyridinium hydroxide, adenine, guanine, cytosine, and thymine.
The nitrogen-containing compounds that can be zwitterionic compounds are nitrogen-containing compounds that can be zwitterionic compounds at a particular pH. Zwitterionic compounds are neutral compounds having formal opposite charges on non-adjacent atoms. Zwitterionic compounds typically contain both an acid moiety and a base moiety, with the pKa of the acid moiety differing from the pKa of the base moiety, such that the compound is zwitterionic when the pH is between the pKa of the acid moiety and the pKa of the base moiety. Zwitterionic compounds also are referred to as inner salts. For example, amino acids are nitrogen-containing compounds that can be zwitterionic compounds, though the nitrogen-containing compounds that can be zwitterionic compounds need not be amino acids. In that respect, as regards the polishing additives identified above, pyridineethanesulfonic acids, pyridine sulfonic acids, pyridyl acetic acids, 3-(3-pyridyl)proprionic acid, pyrazine carboxylic acid, 1-(3-sulfopropyl)pyridinium hydroxide, and picolinic acid are nitrogen-containing compounds that can be zwitterionic compounds. Additional nitrogen-containing compounds that can be zwitterionic compounds, which are useful in the polishing composition of the invention, include sulfanilic acid, dodecyldimethyl(3-sulfopropyl)ammonium hydroxide (lauryl sulfobetaine), (carboxymethyl)trimethylammonium hydroxide (betaine), 2-(N-morpholino)ethanesulfonic acid, N-2-acetamidoiminodiacetic acid, 1,3-bis[tris(hydroxymethyl)methylamino]propane, N-2-acetamido-2-aminoethanesulfonic acid, 3-(N-morpholine)propanesulfonic acid, N-tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid, N-2-hydroxyethylpiperazine-Nxe2x80x2-2-ethanesulfonic acid, N-2-hydroxyethylpiperazine-Nxe2x80x2-3-propanesulfonic acid, N-tris(hydroxyrnethyl)methylglycine, cyclohexylaminoethanesulfonic acid, 3-(cyclohexylamino)propanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, salts thereof, and combinations thereof.
Preferably, the polishing additive is picolinic acid, 2-pyridinecarboxaldehyde, 2-pyridinemethanol, 2,3-pyridinedicarboxylic acid, 2,6-pyridinedicarboxylic acid, 2-pyridylacetic acid HCl, 2-pyridineethanesulfonic acid, 4-pyridineethanesulfonic acid, 1,10-phenanthroline, 1,2-pentadione, sulfanilic acid, pyridinesulfonic acid, salts thereof, and combinations thereof.
The CMP system can comprise any suitable amount of polishing additive(s) of the first embodiment and typically comprises about 0.01 wt. % or more of such polishing additive(s). Preferably, the CMP system comprises about 0.1 wt. % to about 10 wt. % of such polishing additive(s). More preferably, the CMP system comprises 0.1 wt. % to about 2 wt. % of such polishing additive(s).
In a second embodiment of the invention, a polishing additive and a peroxy-type oxidizer are present in the chemical mechanical polishing system. The polishing additive is a metal compound having two or more oxidation states. The polishing additive can be a metal salt or a metal ligand complex. For example, the polishing additive can be an iron, copper, or manganese compound of formula MX, MX2, MX3, or M2X3 where M is Fe, Cu, or Mn, and X is selected from the group consisting of nitrate, fluoride, chloride, bromide, iodide, oxide, hydroxide, sulfate, acetate, oxalate, acetylacetonate, citrate, tartrate, malonate, gluconate, phthalate, succinate, perchlorate, perbromate, periodate, and combinations thereof. The polishing additive also can be a cerium compound of formula CeX2 where X is selected from oxide, hydroxide, and combinations thereof. Preferably, the polishing additive is iron sulfate, iron nitrate, copper nitrate, or manganese perchlorate. The CMP system may contain one or more polishing additives and may contain mixtures of the polishing additives described above.
The CMP system can comprise any suitable amount of polishing additive(s) of the second embodiment and typically comprises about 0.0001 wt. % or more of such polishing additive(s). Preferably, the CMP system comprises about 0.001 wt. % to about 5 wt. % of such polishing additive(s). More preferably, the CMP system comprises 0.001 wt. % to about 2 wt. % of such polishing additive(s).
In a third embodiment, an abrasive is present in the chemical-mechanical polishing system and is suspended in the liquid carrier. The abrasive mixture comprises xcex1-alumina and fumed alumina. Typically, the weight ratio of xcex1-alumina to fumed alumina is about 0.6:1 to about 9:1. Preferably, the weight ratio of xcex1-alumina to fumed alumina is about 1:1 to about 4:1 (e.g., about 1.5:1 to about 3:1).
The CMP system of the third embodiment optionally further comprises a polishing additive. The polishing additive can be any suitable polishing additive. For example, the polishing additive can be any of the polishing additives discussed above with respect to the first and second embodiments. Suitable polishing additives further include carboxylates and acids thereof, hydroxylates and acids thereof, carbonylates and acids thereof, pyrophosphates, condensed phosphates, phosphonic acids and salts thereof, amines, amino alcohols, amides, imines, imino acids and salts thereof, nitriles, nitros, thiols, thioesters, thioethers, carbothiolic acids and salts thereof, carbothionic acids and salts thereof, thiocarboxylic acids and salts thereof, sulfonic acids and salts thereof, thiosalicylic acids and salts thereof, and mixtures thereof
The CMP systems optionally further comprise a per-type oxidizer. The CMP system of the second embodiment comprises a peroxy-type oxidizer.
The per-type oxidizer can be any suitable per-type oxidizer. Suitable per-type oxidizers include inorganic and organic per-compounds. A per-compound (as defined by Hawley""s Condensed Chemical Dictionary) is a compound containing at least one peroxy group (xe2x80x94Oxe2x80x94Oxe2x80x94) or a compound containing an element in its highest oxidation state. Examples of compounds containing at least one peroxy group include but are not limited to hydrogen peroxide and its adducts such as urea hydrogen peroxide and percarbonates, organic peroxides such as benzoyl peroxide, peracetic acid, and di-tert-butyl peroxide, monopersulfates (SO52xe2x88x92), dipersulfates (S2O82xe2x88x92), and sodium peroxide. Examples of compounds containing an element in its highest oxidation state include but are not limited to periodic acid, periodate salts, perbromic acid, perbromate salts, perchloric acid, perchlorate salts, perboric acid, perborate salts, and permanganates. The per-type oxidizer preferably is selected from the group consisting of hydrogen peroxide, persulfate salts (e.g., ammonium persulfate), periodate salts, and permnanganate salts. More preferably, the per-type oxidizer is ammonium persulfate or hydrogen peroxide.
The peroxy-type oxidizer is a compound containing at least one peroxy group and is selected from the group consisting of organic peroxides, inorganic peroxides, and mixtures thereof. Examples of compounds containing at least one peroxy group include but are not limited to hydrogen peroxide and its adducts such as urea hydrogen peroxide and percarbonates, organic peroxides such as benzoyl peroxide, peracetic acid, and di-tert-butyl peroxide, monopersulfates (SO52xe2x88x92), dipersulfates (S2O82xe2x88x92), and sodium peroxide. Preferably, the peroxy-type oxidizer is hydrogen peroxide.
The CMP systems can contain any suitable amount of per-type or peroxy-type oxidizer. The CMP system preferably comprises about 0.5 to about 20 wt. % per-type oxidizer with the polishing additive(s) of the first embodiment. The CMP system preferably comprises about 0.1 wt. % to about 20 wt. % (e.g., about 1 wt. % to about 10 wt. %) peroxy-type oxidizer with the polishing additive(s) of the second embodiment. The CMP system preferably comprises about 0.5 to about 20 wt. % per-type oxidizer with the abrasive of the third embodiment.
The CMP systems of any of the above embodiments desirably have a pH of about 2 to about 12. The actual pH range will depend at least upon the type of substrate being polished. When the CMP system is used to polish a platinum-containing substrate, the pH is desirably about 2 to about 7. When the CMP system is to polish a ruthenium-containing substrate, the pH is desirably about 5 or more, preferably about 7 to about 11. When the CMP system is used to polish an iridium-containing substrate, the pH is desirably about 5 to about 12, preferably about 7 to about 9. While the use of a higher pH tends to increase the removal rate of the noble metal, the removal rate of silicon dioxide layers similarly increases resulting in an overall decrease in the polishing selectivity.
The CMP systems of any of the above embodiments optionally further comprise an amine-containing monomeric, oligomeric, or polymeric compound which helps to reduce the removal rate of a silicon dioxide layer. Suitable amine-containing compounds include polyethylenimine, dimethylaminopropylamine, 1,4-bis(3-aminopropyl)piperazine, and the like.
The CMP systems of any of the above embodiments desirably are used in a method of polishing a substrate comprising at least one noble metal layer and optionally an insulating layer, whereby the substrate is contacted with the chemical-mechanical polishing system and at least a portion of the metal layer or insulating layer (if present) of the substrate is abraded such that the metal layer or insulating layer becomes polished. The substrate can be any suitable substrate (e.g., integrated circuit, memory or rigid disk, metal, ILD layer, semiconductor, micro-electro-mechanical system, ferroelectric, magnetic head, polymeric film, and low or high dielectric constant film) and can contain any suitable noble metal or noble metal alloy layer (e.g., metal conductive layer). The insulating layer can comprise any suitable insulating material, such as a metal oxide, porous metal oxide, glass, organic polymer, fluorinated organic polymer, or any other suitable high or low-xcexa insulating material. The insulating layer preferably comprises a silicon-based metal oxide. The noble metal, noble metal alloy, or noble metal oxide layer preferably comprises platinum (Pt), iridium (Ir), rhenium (Re), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), osmium (Os), or gold (Au). Preferably, the noble metal or noble metal alloy layer comprises platinum, ruthenium (e.g., RuO2), or iridium (e.g., IrO2).